Best PSU for my build?

jimbles

Reputable
Apr 8, 2014
16
0
4,510
(just to get it out of question, I cannot custom-build my rig, long story)

I am purchasing this prebuilt computer to use as a starter base for upgrades.

http://www.bestbuy.com/site/desktop-8gb-memory-1tb-hard-drive/1822053.p?id=1219065404328&skuId=1822053&st=m51bc&cp=1&lp=6

Upon buying it, I intend on adding
Cooler Master Hyper 212 EVO
GTX 770 4GB

Originally I would have purchased an Antec HCG-620M PSU to go along with it, but I'm not entirely sure 620 watts is enough.
I'd like to know the best PSU to add to my rig.